1. Field of the Invention
The invention relates to a device for measuring the spatial distribution of radiation absorption in a slice of a body, said device comprising a radiator (for example, an X-ray tube) for generating a fan-shaped radiation beam for irradiating the body, a row of adjacently arranged radiation detectors for determining measuring values concerning the radiation emerging from the body, the measurements being performed in a number of different angular positions of the radiator/detector system with respect to the body, the direction of the radiation beam extending in the slice of the body, and also comprising a reconstruction device for determining the absorption distribution in the slide on the basis of the measuring values obtained. A device of this kind is known from U.S. Pat. No. 3,937,963.
2. Description of the Prior Art
The advantage of a device of this kind over a device comprising only a single detector such as described, for example, in British Patent specification No. 1,283,915, consists in that the measurement can be performed faster, because a large number of measuring values can be simultaneously obtained and because for the measurement of the radiation absorption in the slice it is only necessary to rotate the radiator/detector system about an axis which extends perpendicularly to the slice, preferably through the body to be examined. There is a drawback, however, in that the probability of at least one of the many detectors required being defective is no longer negligibly small. If a detector is defective, the measurement of the absorption on the basis of the measuring values determined by the detectors is disturbed.
A defective detector is not to be understood herein a detector which produces a change of a measuring value due to temperature influences or aging, in which case changes in the order of a few percent of the measuring value occur. Such a fluctuation in the measuring value usually influences all detectors to the same extent. For the correction of such fluctuations, devices are already known (German Offenlegungsschrift No. 25 13 137) which are based on the assumption, however, that the relative fluctuation of a measuring value during the measurement is small. A defective detector is to be understood to mean herein the complete breakdown of a detector or an amplifier associated with this detector, or a sudden and irregular fluctuation of the measuring value thereof at constant X-radiation. Phenomena of this kind can occur, for example, due to partial or complete damaging of a detector by excessive X-radiation, due to mechanical damage or due to incorrect contact connections in the amplifiers associated with the detector.
It has been found that a defect in one or more detectors gives rise to circular or beam-like interference patterns during the reconstruction of the absorption distribution, said patterns making the interpretation of the absorption values thus obtained difficult or even impossible.